1. Field of the Invention
The present invention generally relates to a powered hand tool whose output provides a reciprocating motion. More specifically, this invention relates to a profiler whose reciprocating output is used to reciprocate any one of various attachments which are used to finish contoured surfaces such as those found on a die or mold, wherein a bearing cartridge is provided which better tolerates the cyclic loading transferred through a cam actuated device which produces the reciprocating motion.
2. Description of the Prior Art
As produced, machined and cast articles have generally moderate to poor surface finishes which are nevertheless acceptable for many uses. However, where it is essential that a machined or cast article have a superior surface finish, such as when the article is a die or molding for use in the extrusion or casting of a metal or plastic product, it is imperative that the surface of the article undergo a process which removes any surface irregularities and burrs which would otherwise adversely affect the end product. An appropriate cutting or abrasive tool is used by an operator to carefully remove irregularities from the article's surface, with particular care given to sharp surface contours which are more difficult to form.
To assist in such operations, powered hand tools which provide a reciprocating output, generally referred to as profilers, are known in the art. The reciprocating output of a profiler is used to reciprocate a suitable attachment, such as a cutting or abrasive tool, which can then be directed at the surface areas of the article for which additional surface finishing is needed. Preferably, the stroke length is adjustable with a maximum stroke of approximately one quarter inch being typical.
Essentially, the reciprocating output of the profiler is derived from a drive rod which follows a cam rotated by an external source. Though capabilities vary according to the particular design, speeds of as much as 22,000 rpms are known, with speeds of up to 5,000 rpms probably being the most common and associated with the more durable designs. The external source for rotating the cam can be either a remote hydraulic or electric-powered unit, preferably being equipped with a speed control unit which allows the operator to adjust the profiler's speed according to the finishing process being undertaken. The external source transmits the rotary motion to the cam through a suitable cable, such as a flexible drive shaft protected within a sheath.
An early example of a profiler is illustrated in U.S. Pat. No. 2,690,081 to Bjorklund et al. There, a generally cylindrical housing is shown within which a shaft and cam assembly is longitudinally disposed. The cam reciprocates a radially extending rod one full stroke cycle with each rotation of the shaft. The rod transfers the reciprocating motion to a tool attachment, which in turn reciprocates a tool secured therein. As a consequence of the high side loads transmitted by the rod to the cam and shaft assembly, a pair of bearings are shown in a spaced apart manner to support the shaft. The bearings are spaced apart to minimize stresses which would otherwise be amplified if the shaft were merely supported by a pair of bearings at one end in a cantilever-style arrangement. As shown, the upper bearing absorbs the brunt of the side loading, while the lower bearing primarily acts to stabilize the cam and shaft assembly. A similar bearing arrangement is shown in U.S. Pat. No. 4,233,850 to Edwardson.
A disadvantage with the arrangement taught by Bjorklund et al and Edwardson is that when maintenance is required on the profiler the cam and shaft assembly must be separated from their bearings. Moreover, the upper bearing must be installed well within the housing, making it difficult to both install and provide an adequate fit between the bearing and the housing to prevent movement therebetween. A further disadvantage is that the material removed from the article being finished is able to enter the bore housing the reciprocated rod, which can quickly degrade the components at the speeds at which the profiler operates.
Alternative bearing arrangements are taught in U.S. Pat. No. 3,007,230 to Riedl and U.S. Pat. No. 4,593,579 to Oszut. There, a pair of bearings are positioned on both sides of the cam so as to avoid any cantilever loading on the shaft and better distribute the side load between the bearings. However, access is again complicated for maintenance purposes by requiring that one of the bearings be removed prior to gaining access to the cam device. The procedure for assembling the devices taught by Riedl and Oszut is especially complicated in that the bearings are each retained within a separate housing member, furthering the propensity for the bearings to be misaligned.
U.S. Pat. Nos. 3,626,768 and 4,512,207 to Dancsik illustrate another suggested bearing arrangement, wherein the bearings are mounted close together on only one side of the cam. Though having gained commercial acceptance, it is apparent that the bearings of the Dancsik profiler are required to sustain substantial side loading which is unevenly distributed between the bearings, the bearing closest to the cam sustaining the greatest side load as a result of the shaft being supported as a cantilever. The loading on this bearing is sufficiently high such that significant heat is generated by the rolling resistance of the bearing, particularly in the case of the ball bearing shown due to the point contact between each ball and the race. One problem caused by the heat buildup is the discomfort of the operator while holding the profiler. But, more significantly, the resulting high temperatures shorten the life expectancy of the bearing by reducing the effectiveness of the bearing's lubrication, while also causing the outer race of the bearing to loosen from its pressfit as a result of the differences in the coefficient of expansion between the steel bearing and the aluminum housing in which it is mounted. Loosening of the outer race allows the bearing to rotate adversely affecting the life of the bearing as well as contributing to the already existing localized heat problems. As a result, the bearings are highly susceptible to premature wear and failure, requiring frequent replacement.
A partial solution to this heat problem is to provide a poorly conducting sleeve, such as one made of plastic, which can be fit over the handle of the profiler to protect the operator. However, such a remedy does nothing to dissipate the heat from the bearings. Another attempted solution to this problem has been to remove the side shields on the bearings to allow the heat to dissipate from the rolling elements of the bearings. However, such an attempt has proven to be inadequate in significantly reducing the temperature of the bearings and their environment. Moreover, the lubrication which would otherwise be retained by the shields in the upper bearing tends to migrate downward when the shield is removed, further contributing to the generation of heat and eventual bearing failure. Attempts to ventilate the bearing, including the use of forced air between the bearings, have also proved to be unsatisfactory in that inadequate cooling is achieved.
What can be further seen from the profiler taught by Dancsik is that both bearings must be press fit into a recess which is well within the housing. As a consequence, maintenance and replacement of the bearings is greatly complicated, requiring extra care when removing and installing the bearings so as not to damage the recess in which the bearings are located. Another disadvantage is the possibility of debris contaminating the bore containing the reciprocating rod, leading to degradation of the internal components of the profiler. The passage to which a tool is attached to the profiler acts as an entrance to the interior of the profiler, exposing a spring, ball and the reciprocated rod to highly abrasive contaminants. When an unyielding surface is impacted with the attached tool, the reciprocated rod can be lifted from its seat, allowing the contaminants to enter the housing itself. Consequently, the profiler taught by Dancsik is also highly susceptible to premature wear and failure from contaminants.
From the above discussion, it can be readily appreciated that the prior art does not disclose a profiler which has the advantage of providing a bearing arrangement which facilitates the removal and/or installation of the bearings while also reducing the generation of heat built-up by the bearings as well as is conducive to the dissipation of the generated heat within the environment. Nor does the prior art teach or suggest an effective method for preventing machining abrasives and debris from entering the profiler's housing.
Accordingly, what is needed is a profiler having a rugged design which acts to reduce and better dissipate the heat generated within the bearings which support the cam and shaft assembly, while also effectively protecting the internal components of the profiler from contamination by debris, thus enhancing the maintainability of the profiler, and in particular the removal and replacement of the bearings.